Comparison of Italian and Spanish

Auxiliary Verbs

Spanish has the complication of two verbs meaning 'to be', namely,
ser and estar. The first is used mainly for permanent
states, whereas the second is used mainly for temporary states.
The equivalent verbs essere and stare exist in Italian, but
stare is used much less frequently than estar. Compare the
Italian Dov'&egrave? and Sono stanco with the Spanish
¿Dónde está? and Estoy cansado.

Italian use of stare follows Spanish, however, in the construction
of the gerund (see below) and also in a few set phrases
(compare Sto bene with Estoy bien).

The main verb in Italian meaning 'to have' is avere. In Spanish
it is tener. However, whereas Italian uses avere to form
compound tenses, Spanish does not use tener. Instead, Spanish has
the special auxiliary verb haber.

Italian has three main modal auxiliary verbs: dovere, potere
and volere. One can use some other verbs, such as sapere, as modals.
There are also several impersonal verbs, such as bastare, bisognare,
convenire that behave as modals.

Spanish also has the three modal verbs deber, poder and
querer. However, in Spanish it is common to use tener que in place
of deber. (This is similar to the English 'to have to'.) Impersonal verbs
include haber que and hacer falta.

It should be noted that the Spanish modal querer followed by
a person or animal means 'to love'. (To express a similar sentiment in Italian,
one can use volere bene (a qualcuno).)

For more on the auxiliary verbs essere, avere and
haber, see the page on compound tenses.